Method of manufacturing filter elements

ABSTRACT

A method of manufacturing a slotted filter element comprising the steps of forming opposite sides of the filter elements by respective electrolysis operations carried out to different degrees so that the slots in cross-section are more flared towards one side than the other, and swaging the filter element to give the slot cross-section the form of a single funnel.

ite States atent Guinard 14 1 Jan. 9, 1973 54 METHOD OF MANUFACTURING2,226,383 12/1940 Norris ..204/11 FILTER ELEMENTS 3,044,l67 7/1962Mathiew ..29/l63.5 R x 1 1 1mm P Andre'cuinard, 7 Pom di ZZQZZZS 131132?ii'i'ii i' ariiiiiiiiiiiiiififriifii 3M8), clud France 3,520,418 '7/1970Guinard ..29/l63.5 R x [22] Filed: Nov. 25, 1970 [21] Appl No'f92690Primary ExaminerCharles W. Lanham Assistant Examiner-Victor A. DiPalma[30] Foreign Application Priority Data Attorney-Robert E. Burns andEmmanuel J. Lobato Nov. 27, 1969 France ..6940925 52 user ..29/163.5 F,29/160, 204/11, [571 ABSTRACT 3 A method of manufacturing a slottedfilter element lit, rising th teps of forming pposite ides of the [58]Fleldlof Search "29/1601 1635 11,1635 F; filter elements by respectiveelectrolysis operations 204/111310/498 carried out to different degreesso that the slots in cross-section are more flared towards one side than[56] References the other, and swaging the filter element to give theslot cross-section the form of a single funnel.

3 Claims, 5 Drawing Figures PATENTEDJAH 9 I973 FiG.1

FiG.2

FI'G.3

FiGA

METHOD OF'MANUFACTURING FILTER ELEMENTS FIELD OF THE INVENTION Thisinvention relates to filter strips containing rows of slots ofgeneraloblong or rectangular form, from which strips filters ofgenerally frusto-conical or cylindrical form may be made.

BACKGROUND OF THE INVENTION Such filter strips may be made by punching ametallic strip or formed directly by electrodeposition, the rows ofslots then being subjected to a swaging (i.e. pressure) operation withthe help of a swaging tool so as to reduce the depth and width of theslots while forming, between said slots, linear projections on atleastone of the faces of the strip according to applicants prior US. Pat. No.3,520,418.

To obtain well calibrated slots which, during a filtering or drainingoperation, permit solid particles of predetermined sizes to pass throughthe filter without these particles blocking said slots, it is'desirablefor the cross-section of the slots to include a short portion havingsubstantially parallel walls which then diverge in the direction of flowto form a wide opening. This configuration, having a funnel-shapedcross-section, is obtained prior to swaging, either during the punchingoperation by using punches having the desired crosssection-, or afterpunching, by any appropriate means such as sand-blasting.

SUMMARY OF THE INVENTION The present invention is more particularlyconcerned with the use of a swaging operation for reducing the width ofthe slots in the case of filter plates having parallel rows of slots andmade by an electrolytic method, particularly such a method employingnickel. This method comprises coating a zinc plate with a lightsensitiveelectrically insulating coa n e.g. a varnish, in forming on the layer ofvarnish a negative image of the slotted plate that it isdesiredtoobtain, the zones exposed to the light becoming insoluble, and inremoving the unaffected zones of the coating of varnishby swilling withwater. The face of the zinc plate, that then has insulating zonesoccupying the positions at which it is desired to formthe slots of thefilter, is then covered with a coating of electrically conductingmaterial (e.g. a varnish) and then covered with nickel by electrolysisin a nickel-salt bathin which the plate is immersed, the zinc plateforming the cathode and the nickel being deposited over the entiresurface except for the zones covered by theinsulating varnish andcorresponding to the slots. The slotted nickel foil thus obtained isthen detached from the layer of electrically conducting varnish. Thenickel foil thus obtained has, between the slots, a curved cross-sectionof general semi-circular form (as can be seen in FIG. 1 above line X-X),so that the slots have the required divergent form.

However, if it is required to obtain by this process a foil of adequatethickness and mechanical strength,

prolongation of the operation of electrolysis, while increasing thethickness of the nickel deposit between the slots, also causes nickel tobedeposited on the edges of the slots, this occurring in an irregularfashion sothat the dimensional tolerance on the width of the slots ob- 2tained is too great for many applications, some of which require atolerance not exceeding 0.01 mm; it is clear that a subsequent swagingoperation, though enabling the mechanical properties of the plate to beimproved, cannot eliminate the lack of uniformity in the original slots.

Itis possible to increase the thickness of the nickel foil by a secondoperation of electrolysis by depositing nickel on its. second planarface, that was attached to the electrically conducting varnish duringthe first operation of electrolysis, the nickel foilitself constitutingthe cathode in this second operation. However, the cross-section of theslots thereby acquires the general form of a cotton reel or a doublefunnel because of the curved form of the nickel deposit between theslots, and the swaging operation on the rows of slots does not then makeit possible to obtain slots having a cross-section in the form of ashort inlet portion with substantially parallel walls on one side of thestrip which then diverges abruptly towards the outlet in the directionof flow in the form of a single funnel on the other side of the strip.

The present invention enables these drawbacks to be substantiallyobviated and is mainly characterized in that the filter strip isobtained by a first complete operation of electrolysis which, after thestrip has been turned round, is followed by a second partial operationof electrolysis or vice versa, so that-the cross-sections between theslots provide a general semi-circular form on the first side and asimilar but much flattened form on the second side, these operations ofelectrolysis being followed by swaging of the rows of slots so assubstantially to impart to them the required single-funnel form and toform linear projections on at least one of the faces of the stripsbetween the rows of slots.

In a modified form, this swaging operation involves the use of a backingplate or die having at least one projecting portion between the slots inthe strip, so as to facilitate the formation of a substantiallyparallelwalled section having relatively sharp edges preceding thedivergent portion of each slot.

This modified form employing a backing plate or die havingprojectingportions can be used also when the perforated strips are formed bypunching.

in these modified forms, the projecting portions on the backing plate ordie fon'n burrs at the marginal portions of the'slots, which burrs can,if not required, for a particular application, be removed for example bybuffing. Y

BRIEF DESCRIPTION OF THE DRAWINGS For a better understanding of theinvention reference will now be made to the accompanying drawings,provided merely by way of example, in which:

, FIG. 1 is a cross-section on a very large scale through a filter stripobtained by electrolysis in accordance with FIG. 2 is a viewcorresponding to the FIG. 1, but

after swaging, I q h 7 FIG. 3 is a plan view of the strip shown in FIG.2,

FIG. 4 is a cross-section on the line IV-IV of FIG. 3, I

and

FIG. 5 corresponds to FIG. 3, but shows the result of using a swagingarrangement employing a backing plate or die having projecting portions.1

DESCRlPTlON OF SPECIFIC EMBODIMENT The filter strip 1, shown in FIG. 1,is produced by electrolysis in two successive operations. A firstcomplete operation of electrolysis as described above enables theportion of the strip located above the line X-X to be obtained. Afterthe strip has beenturned round, a second electrolysis operation iscarried out as already described, but in accordance with the inventionthis is arrested before its final stage, which enables the strip to becompleted by addition of the portion below the line X-X.

It will be observed, that on either side of the line X- X in FIG. 1, theslots 2 have enlarged shapes 2A and 2B, but the portion 2B, locatedbelow the line X-X and corresponding to the incomplete operation ofelectrolysis, is much less accentuated. The two different degrees ofelectrolytic deposition can be carried out in the opposite order.

When swaging is carried out, this smaller widened portion 23 ispractically eliminated so that it has substantially parallel walls asseen in particular in FIG. 2.

The swaging operation, in which a swaging tool that is slightly widerthan the length of the slots 2 is employed, enables projecting portions3 to be formed between the rows of slots 2, these projecting portionsstrengthening the filter strips while permitting the entirety of theslots to be employed. Furthermore, this swaging operation on the filterstrips obtained by electrolysis improves the quality of the metal, thegranular structure of which is converted into a lamellar structure,which imparts greater rigidity to the strip while improving its elasticproperties and its wear-resistance because of the workhardening of themetal which imparts greater hardness to the surfaces.

To facilitate deformation and flow of the metal in the zone 2B, so as toprovide the short substantially parallel-walled portion of the slot, abacking plate or ,die employed in the swaging operation can have slightprojections located between the slots, which projections then impart tothe filter strip 1 the form illustrated in FIG. 5 in which theseprojecting portions form slightly concave areas 4 with raised portions 5at the slot edges. This modified form of the swaging operation can alsobe employed on filterstrips obtained by punching as previouslyindicated.

When the filter is in use, these slightly concave areas 4 between theraised portions or burrs 5 permit a layer of the treated product toaccumulate and this inhibits wear on the filter. In certain cases, anddepending upon the nature of the productstreated, it is desirable toprevent this accumulation; then, the burrs 5 can simply be removed, by abuffing operation for example.

The present invention also comprises filter plates or stripsobtained bythe above-described method, as well as cylindrical or frusto-conicalfilters particularly for centrifugal draining systems formed byassembling and bending said plates or strips.

I claim:

1. A method of producing a filter element, said filter element having afirstand a second side and a plurality of parallel rows of slotstherein, each slot extending through the filter element from the firstside to the second side, the method comprising the steps of forming afirst slotted portion of the filter element at the first side thereof bya first electrolysis operation, adding a if$3ll$22ill 3Pi2ll1illli ,Emeans of a second electrolysis operation, said first and secondelectrolysis operations being carried out to different degrees toproduce on said first side slots separated from one another by partshaving in crosssection a substantially semicircular convex form, andonsaid second side slots separated by parts having in cross-section asimilar convex but considerably flattened form, and swaging the partlyformed filter element so that the slots acquire a cross-section in theshape of substantially'a single funnel divergingfrom said second sidetowards said first side and linear projecting portions are formed atleast on the first side of the element between rows of slots. 1

2. A method of producing filter elements as claimed in claim 1, whereinthe swaging operation involves the use of a backing member havingprojections located between the slots to facilitate the formation of asubstantially parallel-walled section of each slot having relativelysharp edges at said second side of the filter element. I

3. A method of producing filter elements as claimed in claim 2, whereinthe projections on the backing member form burrs at the marginalportions of the slots on said second side.

l III

2. A method of producing filter elements as claimed in claim 1, whereinthe swaging operation involves the use of a backing member havingprojections located between the slots to facilitate the formation of asubstantially parallel-walled section of each slot having relativelysharp edges at said second side of the filter element.
 3. A method ofproducing filter elements as claimed in claim 2, wherein the projectionson the backing member form burrs at the marginal portions of the slotson said second side.